linux-kernel - Re: [PATCH 1/2] PCI: AtomicOps: Define valid root port capabilities

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Message-ID: <20251110140211.GK15456@unreal>
Date: Mon, 10 Nov 2025 16:02:11 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Gerd Bayer <gbayer@...ux.ibm.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
	Jay Cornwall <Jay.Cornwall@....com>,
	Felix Kuehling <Felix.Kuehling@....com>,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	Alexander Schmidt <alexs@...ux.ibm.com>, linux-s390@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] PCI: AtomicOps: Define valid root port capabilities

On Mon, Nov 10, 2025 at 02:25:05PM +0100, Gerd Bayer wrote:
> Provide the two combinations of Atomic Op Completion size attributes
> that a root port may support per PCIe Spec 7.0 section 6.15.3.1. -
> besides the trivial "No support" - as two new defines.
> 
> Change documentation of pci_enable_atomic_ops_to_root() that these are
> the only ones that should be used. Also, spell out that all requested
> capabilities need to be supported at the root port for enable to
> succeed. Also emphasize that on success, this sets AtomicOpsCtl:ReqEn to
> 1, and leaves it untouched in case of failure.
> 
> Suggested-by: Leon Romanovsky <leon@...nel.org>
> Signed-off-by: Gerd Bayer <gbayer@...ux.ibm.com>
> ---
>  drivers/pci/pci.c             | 13 +++++++------
>  include/uapi/linux/pci_regs.h |  8 ++++++++
>  2 files changed, 15 insertions(+), 6 deletions(-)

<...>

> +/* PCIe spec 7.0 6.15.3.1: Root ports may support one of 2 sets of Atomic Ops */
> +#define  PCI_EXP_ROOT_PORT_ATOMIC_BASE		\
> +	(PCI_EXP_DEVCAP2_ATOMIC_COMP32 |	\
> +	 PCI_EXP_DEVCAP2_ATOMIC_COMP64)
> +#define  PCI_EXP_ROOT_PORT_ATOMIC_FULL		\
> +	(PCI_EXP_DEVCAP2_ATOMIC_COMP32 |	\
> +	 PCI_EXP_DEVCAP2_ATOMIC_COMP64 |	\
> +	 PCI_EXP_DEVCAP2_ATOMIC_COMP128)

Thanks for doing this.